Sargassum

 Sargassum

Systematic Position :

Division : Phaeophyta

Class : Cyclospoae

Order : Fucales

Family : Sargassaceae

Genus : Sargassum

This genus comprise more than 150 species which are chiefly distributed in tropical and sub tropical seas of the Southern hemisphere. they are found in the form of huge floating masses in the Atlantic Ocean, hence this part of ocean is called Sargasso Sea . In India, this genus in represented by 16 species, which are found along the Western and Southern coasts. On the Western coast it is found at Okha, Dwarka, Mumbai Porbandar, Karwar, Mangalore and Malven, while on Southrn coasts it is available at pamban, Krusadai and Tuticorin, Sargassum is the most common marine brown alga of indian  ocean. The common India specient are Sargassum carpophyllum and S. plagiophyllum.

Thallus Organisation

External Morphology

        The plant body is sporophytic and diploid in genetic constitution. It is differentiated into main axis and hold fast the main aixs bears laterall branches and air bladders

The hold fast is warty or discoid structure meant for acnhorage or fixation. In some species it is stolon like. The main axis or stem consists of erect, flagttend or cylindrical strutures and attains a height of 15 to 25 cm. In S. fillipendula, it is more than one meter and bears large numbers of primary laterals in in spiral fashion. These primarly laterals have unlimited growth, hence they are called long shoots. the primary laterals in turn produce leaf like branches which are called secondary laterals or leaves 

    The leaves of majority of the species of Sargassum are simple, with distinct midrib, but in some mid-rib, is absent as in S. enerve. The margin is usually engtire, serrate or dentate, The leaves possess small pores on the upper surface known as ostioles these pores open in small flask shaped cavities known as cryptostomata or sterile conceptacles .

Towards the basal part of the primary part of the primar laterals, rudimentary axillary branches are present and the upper.portion possesse axillary branch system. From the axillary branches, one or two branches Cryptostomate basal get modified into globula or spherical air bladders  Lateral (leaf) These air bladders filled with air, help the plant in floating by increasing buoyancy. In some members, air bladders get modified into leaf like Receptacular brancn Air bladder Axis Sargassum: Thallus showing receptacular branch. structure. It is also reported by some algalogists that the air bladders help in respiration. In majority of the species, the axillary branch system develops into long, cylindrical structure known as receptacles. These receptacles bear reproductive structures in special flask shaped cavities the conceptacles. The growth of the thallus takes place by an apical cell, which is quadrangular in shape. 

 Internal Structure 

 Internal Structure of Main Axis:

 Atransverse section of main stem of Sargassum reveals the following tissue organisation. The whole tissue is dififerentiated into three distinct regions viz. meristoderm, cortex and medulla  Meristoderm: It forms the outermost, single, epidermis like layer. The cells are columnar and are arranged compactly. They are densely packed with chromatophores and contain fucosan as reserve food material. It forms the assimilatory region of the stem and in mature part, it is covered by mucilagenous cuticle. Cortex: It forms major portion of the axis, the cells are narrow and elongated, loosely arranged, with well developed intercellular speces. 1ne ells contain reserve food material. Medulla: It forms, the central core of the axis. It is made up of thick alled, elongated cells which sometimes show scalariform thickening